U.S. Pat. No. 4,169,371 discloses a method and apparatus for producing signals proportional to the rotational speed of an engine and signals proportional to the torque of the engine. A single sensor senses pulses generated by an ignition coil driven by the engine, the sensor producing first output signals proportional to engine speed. The first signals are differentiated to obtain second signals proportional to engine acceleration. The second signals are multiplied by a constant representing the moment of inertia of the engine to thereby provide an indication of engine torque. The patented device is intended for torque measurement of an unloaded engine or, at best, an engine loaded only by the power transmission system. Since torque may be measured only during engine acceleration the primary use of the device is for engine characteristic analysis or diagnostic purposes and it is not suitable for real time control in a moving vehicle.
U.S. Pat. No. 4,691,288 discloses a system, suitable for use under normal conditions such as when the vehicle is on the road, and providing indications of engine speed and torque. This system, which requires an index wheel and timing teeth on a flywheel, must have two sensors for sensing the index and the timing teeth. In this system torque is determined from average engine speed and subcyclic engine speeds.
It is conventional to provide a large mass, commonly called a flywheel, on the crankshaft of an engine, the inertia of the flywheel tending to cause more uniform velocity of the crankshaft even though the crankshaft receives power in pulses as each cylinder fires. It is also known to provide a damper between the engine and the input shaft of a powershift transmission in an agricultural tractor, the damper tending to deflect and thus absorb the power pulses so that the torque delivered to the transmission input shaft is more constant over an engine cycle.